Increasing the Scale of Successful Invasive Rodent Eradications in the Galapgaos Islands Karl J
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GALAPAGOS REPORT 2011-2012 BIODIVERSITY AND ECOSYSTEM RESTORATION INCREASING THE SCALE OF SUCCESSFUL INVASIVE RODENT ERADICATIONS IN THE GALAPGAOS ISLANDS KARL J. CAMPBELL , VICTOR CARRIÓN AND CHRISTIAN SEVILLA How to cite this document GNPS, GCREG, CDF, and GC. 2013. Galapagos Report 2011-2012. Puerto Ayora, Galapagos, Ecuador. How to cite this article Campbell KJ, V Carrión and C Sevilla. 2013. Increasing the scale of successful invasive rodent eradications in the Galapagos Islands. Pp. 194-198. In: Galapagos Report 2011-2012. GNPS, GCREG, CDF and GC. Puerto Ayora, Galapagos, Ecuador. Sources must be cited in all cases. Sections of the publication may be translated and reproduced without permission as long as the source is cited. The authors of each article are responsible for the contents and opinions expressed. The Galapagos National Park Service has its headquarters in Puerto Ayora, Santa Cruz Island, Galapagos and is the Ecuadorian governmental institution responsible for the administration and management of the protected areas of Galapagos. The Governing Council of Galapagos has its headquarters in Puerto Baquerizo Moreno, San Cristóbal Island, and is the Ecuadorian governmental institution responsible for planning and the administration of the province. The Charles Darwin Foundation , an international non-profit organization registered in Belgium, operates the Charles Darwin Research Station in Puerto Ayora, Santa Cruz Island, Galapagos. Galapagos Conservancy , based in Fairfax, Virginia USA, is the only US non-profit organization focused exclusively on the long-term protection of the Galapagos Archipelago. GALAPAGOS REPORT 2011 - 2012 Increasing the scale of successful invasive rodent eradications in the Galapagos Islands Karl J. Campbell1,2, Victor Carrión1,3 and Christian Sevilla3 1Island Conservation, 2School of Geography, Planning and Environmental Management, The University of Queensland, 3Galapagos National Park Service Julia Ponder with the twentieth Background Galapagos hawk placed in temporary captivity. Introduced rodents are major drivers of extinctions on islands, impact agricultural Photograph: ©Rory Stansbury, production, consume and spoil stored foods, and spread diseases that impact Island Conservation human health (Towns et al., 2006; Varnham, 2010). Introduced rodents impact the reproduction of native vegetation through seedling and seed predation, and prey on invertebrates, land and seabirds, and reptiles (Towns et al., 2006). In Galapagos, introduced rodents have negatively impacted natural ecosystems by contributing to the extinction of endemic rice rats, declines in giant tortoise populations, and declines and extirpations of land and seabirds and other fauna (Cruz & Cruz, 1987; Dowler et al., 2000; MacFarland et al., 1974; Steadman & Stafford, 1991). By consuming seeds and seedlings they impede regeneration and alter forest dynamics, affecting entire ecosystems (Clark, 1981). Impacts on invertebrates have not been quantified in the Galapagos but likely occur based on impacts elsewhere (Towns et al., 2006). The eradication of invasive rodents is possible; over 360 rodent eradications on islands worldwide have been successful to date. Anticoagulant rodenticides have made these eradications possible, using aerial bait application methods on large islands and those with rough terrain. Rodent eradications on islands as large as 11,300 ha (Campbell Island, New Zealand with Rattus norvegicus) have been successful. Success of a recent eradication attempt on the even larger Macquarie Island, Australia (12,870 ha), with both mice (Mus musculus) and black rats (Rattus rattus) is awaiting confirmation. Rodent eradication allows extant plant and animal populations to recover, creates additional habitat for extirpated species, which can then recolonize or be reintroduced, and provides rodent-free habitat for conservation introductions to occur (Bellingham et al., 2010). In 2007, a roadmap for a programmatic step-by-step approach to introduced rodent eradications in Galapagos was developed to prevent imminent extinctions (FCD / SPNG 2007). Each step builds local capacity and knowledge, and each subsequent step involves progressively larger and more complex eradications. In late 2007, a hand-baiting rat eradication on North Seymour Island (184 ha) was successful. We report here on the second step, in 2011, involving the aerial broadcast of bait to target three introduced rodent species on Rábida, Bartolomé, Sombrero Chino, and nine smaller islands. Methods and results Since the North Seymour rat eradication was completed in 2007, more than two years of planning, trials and groundwork were required to prepare for aerial 194 GALAPAGOS REPORT 2011 - 2012 Photograph: Rory Stansbury, Island Conservation baiting operations. Bait color choice trials with finches Hawks were also present on other islands to be targeted determined that blue baits were least preferred by - Rábida, Bainbridge #3, and Bartolomé, all of which form finches, and baits in this color would therefore minimize part of the Santiago Hawk population. To build capacity risk to finches (Carrión Bonilla, 2009). Blue non-toxic bait in hawk mitigation measures leading up to Pinzón it was uptake trials with mockingbirds, finches, other land birds, decided to capture and temporarily hold hawks from lava lizards and tortoises were conducted. A toxic bait trial these islands in captivity until the risk to hawks from using Conservation 25D (Bell Laboratories, Wisconsin), a eating toxic rodent carcasses and other prey was minimal. cereal bait with 25 ppm brodifacoum formulated for dry conditions with a pyranine biomarker, was conducted An implementation plan was produced that detailed with before and after monitoring on Plaza Norte, allowing logistics, roles and responsibilities of personnel, baiting for the potential population level impacts of baiting to be rates, and methods, among other details. The operation determined (IC / CDF, 2010). A non-target risk assessment was to be timed during the dry season when natural foods was conducted for all vertebrate species present on Pinzón, for rodents are most limited. The operation was to occur Rábida and other islands proposed for rodent eradication in November 2010, but delays in the contracting of the (Table 1). The assessment determined likely low risk, with helicopter caused the operation to occur in January 2011. high uncertainty, for island endemic Pinzón tortoises The Technical Council of the Galapagos National Park and Pinzón lava lizards. This high level of uncertainty was Service (GNPS) reviewed and validated the non-target considered unacceptable for these island endemics and risk assessment, implementation and hawk mitigation it was recommended to delay implementation on Pinzón plans. In accordance with the implementation plan, and conduct additional trials for these species. Mitigation bait buckets were calibrated on the abandoned airstrip actions proposed for Plaza Sur land iguanas, which have on Baltra with non-toxic bait to ensure buckets would unique genetics (Tzika et al., 2008), also delayed the disperse the precise amount of bait. Two aerially applied proposed eradication of mice from that island. The non- bait applications on the 12 target islands occurred on target risk assessment identified Galapagos Hawks to 7-8 and 14-15 January 2011. Bait was applied using a be at high risk and this was considered unacceptable on helicopter with a bait-spreader bucket flown along pre- Pinzón due to their conservation status and the unique designated GPS lines by a specialist pilot to accurately genetics of the Pinzón population (Bollmer et al., 2006). ‘paint’ the island in parallel swaths. The coast was flown 195 GALAPAGOS REPORT 2011 - 2012 Table 1. Islands proposed for the initial aerial baiting campaign to eradicate rodents. Due to uncertainty of risks to island endemic reptiles and mitigation plans for land iguanas, eradications on Pinzón and Plaza Sur Islands were postponed. No. Island Area (ha) Eradication target 1 Rábida 499 Rattus norvegicus 2 Bartolomé 124 Rattus rattus 3 Islote Gran Felipe 0.4 Rattus rattus 4 Plaza Norte 8.8 Mus musculus 5 Roca Beagle Oeste 4.3 Rattus rattus 6 Roca Beagle Sur 8.7 Rattus rattus 7 Roca Beagle Norte 0.7 Rattus rattus 8 Bainbridge #1 11.4 Rattus rattus 9 Bainbridge #3 w/lagoon 18.3 Rattus rattus 10 Bainbridge #5 4.1 Rattus rattus 11 Bainbridge #6 4.5 Rattus rattus 12 Sombrero Chino 20.9 Rattus rattus Total 705.1 Postponed Islands originally proposed Pinzón 1,815 Rattus rattus Plaza Sur 11.9 Mus musculus with a directional bait bucket to minimize bait entering monitored underwent significant declines; however the marine environment. Each bait application across Short-eared Owls on the treatment islands were likely the 12 islands took two days, and applications were negatively impacted by secondary poisoning. However it seven days apart. Total bait applications were 19-22 kg/ is expected that populations on these islands will quickly ha for most coastal areas and 9-12 kg/ha for inland areas. recover due to immigration. After one year of monitoring, Tourist sites (Rábida, Bartolomé, and Sombrero Chino) Galapagos Hawks have shown a mixed response (Ponder were temporarily closed during the bait application, with & Cunninghame, 2012). On Rábida, only one of the GNPS staff providing interpretation to boat passengers original seven hawks remains; three are confirmed dead, and crews. Informative warning signs were placed at three are missing. However, at least five